High energy synchrotron radiation sources are used for research in materials science, chemistry, physics, medical and biological imaging, geophysics and other fields. Currently under construction is the seven (7) GeV Advanced Photon Source (APS) that will generate high brilliance and intense synchrotron radiation from its insertion devices (IDs), which include a variety of magnetic wigglers and undulators. Essential to the success of the APS is a photon beam position monitor (PBPM) that is sensitive enough to locate the position of an X-ray beam with accuracy better than a micron, while withstanding potential damage from the unprecedented heat that could be deposited by an inaccurately steered X-ray beam. The cross-section of a beam can be visualized as having a "core" and a surrounding "halo". The hard X-ray core can cause extremely high heat loads, while the soft X-ray photons in the cooler halo dislodge electrons in metal blades projecting from the PBPM toward the beam. Continuous feedback of the dislodged electron signal correlates with the beam's location.
PBPMs are photo-electron generating components. When a PBPM is placed in the vicinity of a photon beam in ultra high vacuum, photons impinging on the blades of the PBPM knock off electrons in the blade material producing photo-electric currents which are used for determining the position of the beam. There may be two, four or six sets of such blades in a given PBPM, with a minimum of two sets of blades required to sense the beam position per spatial direction (vertical or horizontal). Prior art blades are made out of molybdenum, tungsten, titanium or a titanium alloy TZM. The operating requirements for the blade material are: good photo-electron generation, high thermal conductance and heat resistance, high structural strength, low thermal expansion coefficient, and good X-ray resistance. PBPM blades are typically positioned in the outer 25% of the beam's power envelope so that they are not subject to excessive heat loads which may distort the blade. The blades are also positioned far enough from the beam so as not to be directly hit and damaged by a missteered beam. The blades must remain parallel to the beam so that hot spots and thermal stress do not distort the blades and the blade material must remain rigid at highly elevated temperatures. In addition, thermal effects cause signal drift in these precision devices, with the thermal effects increasing with closer positioning of the PBPM to the beam. Prior art metallic photon detector blades have suffered from a variety of performance limitations in this hostile environment.
The aforementioned problems encountered in the prior art are addressed and resolved by a photon beam position monitor employing a plurality of spaced diamond detector blades each having an outer metal layer which are capable of operating in intense radiation fields in excess of 1250 W/mm.sup.2 while providing sub-micron accuracy in determining photon beam position.